Inorganic polymer based on aluminium and silicon

ABSTRACT

An inorganic polymeric aluminosilicate material and a method for preparing the same, are disclosed. Instead of having a fibrous structure, the material has a structure consisting of spindles with a length in the range of from 10 to 100 μm and a width in the range of from 2 to 20 μm. This polymeric alumino-silicate can be used for the production of antistatic layers.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Divisional of pending U.S. Ser. No. 09/115,879 filed Jan. 30,2001, now allowed, which in turn is a Continued Prosecution Applicationof U.S. Ser. No. 09/115,879 filed Jul. 15, 1998, now U.S. Pat. Ser. No.6,296,825.

FIELD OF THE INVENTION

The present invention concerns a novel polymeric alumino-silicate and amethod for preparing it.

Polymeric alumino-silicates in a fibrous form are known. A fibrous,tubular crystallized alumino-silicate known as imogolite is present inthe impure natural state in volcanic ash and in certain soils.

U.S. Pat. Nos. 4,152,404 and 4,252,779 of Farmer describe an inorganicmaterial similar to natural imogolite. This inorganic material issynthesized by causing silica or a soluble silicate to react with analuminium compound so as to form a complex hydroxyaluminium silicate inaqueous solution with a pH of 3.2-5.5, and then effecting a digestion ofthis complex at a pH of 3.1-5.0 so as to form a colloidal dispersion ofthe inorganic material. This inorganic material can be used as amolecular sieve, a catalyst support, a coagulant or an adsorbent. Byevaporating the colloidal solution of imogolite on a flat surface, it ispossible to form films which can be used as membranes. If the materialis not isolated from its colloidal solution, it can be used as aflocculant, a substance for promoting hydrophilicity or a thickeningagent.

European Patent 0 250 154 describes a photographic product, comprising apolymer surface on which a layer comprising a gelled lattice ofinorganic particles, preferably oxide particles, has been caused toadhere. According to this patent, the gelled lattice forms a porouslayer with voids between the inorganic oxide particles. This porouslayer is obtained from a dispersion or suspension of finely dividedparticles in a liquid medium. The oxide particles can be boehmite(aluminium oxide), silica or a silica gel coated with alumina. Thisgelled lattice is formed by the aggregation of colloidal particlesbonded together in order to form a porous three dimensional lattice.This gelled lattice provides a substratum endowed with antistaticproperties.

European Patent Application 0 741 668 describes a homogeneous polymericalumino-silicate having antistatic properties, as well as a method forobtaining this alumino-silicate with a high degree of purity. Accordingto European Patent Application 0 741 668, the method for obtaining thepolymeric alumino-silicate comprises:

(a) the treatment of a mixed aluminium and silicon alkoxide with anaqueous alkali at a pH in the range of 4 to 6.5, maintaining the Almolar concentration between 5×10⁻⁴ and 10⁻² M and the Al/Si molar ratiobetween 1 and 3;

(b) the heating of the mixture obtained from step (a) to a temperaturebelow 100° C. in the presence of silanol groups, for a sufficient periodfor obtaining a complete reaction and the formation of an inorganicpolymer, and

(c) the elimination of the residual ions from the reaction medium.

The inorganic polymer is a fibrous alumino-silicate of formula AlxSiyOzwhere x is in the range of from 1 to 3 and z is in the range of from 1to 10.

The object of the present invention is a polymeric alumino silicate,derived from the polymeric alumino-silicate of aforementioned PatentApplication 0 741 668, and a method for obtaining this derived material.

The material of the invention is a polymeric alumino-silicate materialof formula AlxSiyOz, in which x:y is a number from 1 to 3 and z is anumber from 1 to 10, this material being substantially comprised ofspindles with a length L of between 10 and 100 μm, a maximum width 1 ofbetween 2 and 20 μm, the ratio L:1 being a number from 3 to 10.

Preferably, x:y is a number from 1.5 to 2.5, z a number from 2 to 6, Lis between 20 and 80 μm and 1 is between 5 and 15 μm.

The terms “substantially comprised” mean that the material comprises atleast 95 weight % and preferably at least 99 weight % of said aluminosilicate spindles, based in the total weight of the material.

The method for obtaining the material of the invention comprises thesteps of:

(a) treating a mixture of an aluminium compound and a silicon compound,both hydrolysable, or a hydrolysable mixed compound of aluminium andsilicon, by an aqueous alkali, at a pH in the range of 4 to 6.5,maintaining the Al concentration between 5×10⁻⁴ M and 10⁻² M and theAl:Si molar ratio between 1 and 3;

(b) heating the mixture obtained from (a) at a temperature below 100° C.in the presence of silanol groups, for a period sufficient forobtaining, by means of a complete reaction, the formation of a polymericalumino-silicate in solution;

(c) concentrating the solution obtained from (b) so as to obtain anAl+Si concentration of at least approximately 1.5 g/l,

(d) settling the concentrated solution obtained from step (c) to produce2 phases, and collecting the upper (less dense) phase, which representsat least 90% and preferably at least 95% by weight polymericalumino-silicate with a spindle morphology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a device for obtaining the material of the invention.

FIGS. 2-3 depict electron microscopy photographs showing the structureof the material of the invention, and FIG. 4 shows the difference inviscosity between the two materials (bunches versus fibres).

DETAILED DESCRIPTION OF THE INVENTION

The steps (a) and (b) of the method are identical to those described inthe aforementioned European Patent Application 0 741 668. The productobtained at the end of step (d) can then be concentrated further inorder to be transformed into a gel, which can itself be freeze-dried, inthe form of a dry powder. This powder can be put back in solution and,in this case, the material put back in solution still has a spindlemorphology. It is also possible, after step (d), to eliminate the ionsand the small molecules present in the concentrated solution and,essentially from the alkali used. This elimination can be carried out bydialysis.

The novel material according to the invention is in the form ofspindles. This morphology can be revealed by optical microscopy oratomic force microscopy (AFM), as the photographs in FIGS. 2-3 show.

The method of the invention provides, as indicated, a so-called “upper”phase, consisting of the polymeric alumino-silicate in spindle form anda so-called “lower” phase, which consists of the fibrous polymericalumino-silicate described in the aforementioned European PatentApplication 0 741 668. These two materials have the same basic formulaAlxSiyOz indicated above, confirmed by the same Raman spectrum, and aredistinguished from each other by various characteristics such as theviscosity or wetting angle, as shown by the following examples.

According to one embodiment, the solution obtained at b) is concentratedby ultrafiltration on a membrane. The solution obtained at (b) has apolymeric alumino-silicate (Al+Si) concentration which is generallybelow 0.5 g/l. It is necessary to concentrate it so that thealumino-silicate content is greater than 1.5 g/l and preferably greaterthan 1.7 g/l. It is possible to use either a tangential ultrafiltrationmodule in which the solution is pumped at high speed along the membrane,or a frontal ultrafiltration module in which the solution is pumped, ata greater pressure, perpendicular to the membrane. The ultrafiltrationmembranes which can be used for this purpose are for example cellulosicmembranes such as the 10 KD membrane sold by AMICON, polyethersulphurmembranes such as the membrane 100 KD sold by MILLIPORE, orpolyacrylonitrile membranes.

According to another embodiment, the solution obtained at the end of theabove step (b) can be concentrated by distillation.

A preferred embodiment consists of concentrating the solution obtainedat step (b) by tangential ultrafiltration on a cellulosic membrane. Suchan embodiment is depicted schematically in FIG. 1. According to thisdiagram, the solution 10 coming from step (b) is sent by pumping(pumping unit 12 with pump 13 and flowmeter) into an ultrafiltrationmodule 14 fitted with a spiral membrane. The permeate is dischargedthrough the pipe 15 and the enriched retentate of the desired phase ofthe alumino-silicate is sent at 10 through the duct 16. The inletpressure is between 0.5 and 5.0 bars and the concentration factor isbetween 30 and 60%, advantageously around 40%.

EXAMPLE 1

A solution of 5 liters of AlCl₃, 6H2O (7.3 g/l) and a solution of 5 l ofSi(OCH₃)₄ (2.56 g/l) in osmosed water were prepared. These solutionswere mixed and 370 ml of NaOH 1M were added dropwise. The mixture waskept overnight under stirring. The pH was adjusted to 6.8 with NaOH anda gel was obtained. This gel was diluted in 5 l of osmosed water,acidified by 25 ml of a mixture of HCl 1M and CH₃CO₂H 2M. This mixturewas stirred until a transparent solution was obtained. The transparentsolution was diluted with 11 liters of osmosed water, and then heated at96° C. for 5 days in the presence of finely divided silica. A solutionof 0.3 g/l of polymeric alumino-silicate was obtained.

Using a tangential ultrafiltration module as depicted in FIG. 1, thepolymeric alumino-silicate solution was concentrated. Theultrafiltration module 14 comprised a regenerated cellulose woundmembrane 10 KD sold by AMICON. Ultrafiltration was carried out at apressure of 0.7 bar. After concentration, the retentate comprised 4.4g/l of alumino-silicate.

After this retentate was allowed to stand overnight, two separate phaseswere formed. The less dense upper phase was separated from the lowerphase.

Characterisation of the two phases gave the following results:

Refrac- Resistivity Al:Si Al:Si tion Water Decane G ICP TEM indexadhesion adhesion ohm/m² Upper phase 1.93 2.11 1.335 yes yes 3containing spindles (invention) Fibrous 2.01 2.14 1.335 no yes 11 lowerphase

A sample of ESTAR® polyester film support was coated at 100 mg/m², witheach of the two phases and then examined under optical microscopy andAFM. Under AFM (Atomic Force Microscopy) microscopy, a fine tip took areading on the surface of the material by contact. A relief image of thedeposition of polymeric alumino-silicate was obtained. The optical andAFM microscopy photographs obtained are shown respectively in FIGS. 2-3.

The Al:Si ratio was measured both by atomic emission spectroscopy withinductive coupling plasma (ICP) and by EDX spectrometry.

The water/decane adhesion was evaluated by coating an ESTAR®polyethylene terephthalte support film with a layer of the concentratedsolution and then by spraying water or decane onto the coated support.

The resistivity was measured as follows: calibrated strips (2.7 cm×3.5cm) of ESTAR support were produced, coated with the concentratedsolution at 100 mg/m²; these calibrated strips were placed on electrodesbetween which a voltage was established whilst maintaining constanthumidity and temperature (HR 30%−23° C.).

The viscosity was also measured on a CONTRAVES 115 flowmeter as afunction of the stresses applied. The speed of flow curves depicted inFIG. 4, for the solutions of alumino-silicate in spindle form andalumino-silicate in fibrous form, showed that the spindle phase had aviscosity greater than the fibrous phase. Given its resistivity,wettability and viscosity, the solution of polymeric alumino-silicate inspindle form can be used for antistatic layers intended for example forphotographic materials.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A polymeric inorganic alumino-silicate materialof formula AlxSiyOz in which x:y is a number from 1 to 3 and z is anumber from 1 to 10, this material having a gel structure and beingcomprised substantially of spindles with a length L of between 10 and100 μm, a maximum width 1 of between 2 and 20 μm, the ratio L:1 being anumber from 3 to
 10. 2. The material of claim 1, wherein x:y is in therange of from 1.5 to 2.5 and z is in the range of from 2 to
 6. 3. Thematerial of claim 1, wherein the spindles have a length in the range offrom 20 to 80 μm and a width in the range of from 5 to 15 μm.